Recently, a luminaire employing a light emitting device (LED) has been widely used as a light source for illumination. Accordingly, there is a growing demand for luminaires with high-functionality and low-cost. Compared to incandescent lights and discharge lamps, it is possible to more freely and easily control a color of light and perform lighting control (dimming) and mixing colors depending on the situation by using the LEDs, which has led to the development of various luminaires using LEDs.
These kinds of luminaires employ technologies which combine different colored LEDs to obtain a desired color of light and/or technologies which control a light emitting period of time and a light-emitting start timing. FIG. 11 illustrates an example of a conventional lighting system and a conventional luminaire, which are disclosed in, e.g., Japanese Patent Application Publication No. 2011-34780.
FIG. 11 illustrates a block diagram of a conventional lighting system and a conventional luminaire.
The conventional luminaire 100 includes a plurality of LEDs 200 having different colors such as red, green, and blue, and adjusts light outputs of the LEDs 200 to synthesize a desired chromaticity. In addition, the luminaire 100 includes a lighting system 300. The lighting system 300 includes a light receiving element A for measuring an amount of light emitted from each of the LEDs 200; a control unit such as a micro-computer 600 which controls periodical turning on/off of the LEDs 200 or a light-emitting time period of one cycle; and a driving circuit 700.
In the conventional luminaire 100, a current flowing in each of the LEDs is set to a predetermined value and a pulse width modulation (PWM) control is performed. Accordingly, each of the LEDs 200 is periodically turned on and off and a ratio of the light-emitting time period to one cycle (hereinafter, referred to as ‘on duty ratio’) is controlled with respect to each of the LEDs 200, thereby controlling the light output of each LED 200. In the luminaire 100, further, based on the amount of light measured by the light receiving element A, a light-emitting start time of one of the LEDs 200 is controlled to be faster than those of the other LEDs. As a result, it is disclosed that the one LED emits the light solely.
The conventional luminaire 100 obtains a desired chromaticity by measuring an amount of light emitted from the plurality of LEDs 200 using one light receiving element A and adjusting light-emitting start timings of the plurality of LEDs 200 periodically turning on and off. However, in order to obtain the desired chromaticity, the luminaire 100 is required to have the expensive light receiving element A. In addition, since there is a need of periodically turning on and off the LEDs 200, flickering is easy to occur.